It is known in motor vehicles to provide a side door slidably mounted on tracks for fore and aft sliding movement between open and closed positions. As the door reaches the closed position a weatherstrip is compressed to provide weather tight sealing, and a door latch is latched to retain the door in the closed position. In order to obtain such latching of the door and compression of the weatherstrip, the vehicle user slides the door rapidly toward the closed position.
It is also known to provide a motorized mechanism for moving such a sliding door. In particularly it is known to use motor driven pulleys to wind and unwind cables attached to the door, with one cable for pulling the door forward, and another cable for pulling the door rearward.
It is necessary and desirable that such power door closing systems control the closing speed of the door. The vehicle user wishes the door to move at a rapid speed which expedites vehicle ingress and egress, and yet without slamming the door. It is also necessary to control the closing force of the door so that the door is closed with force sufficient to latch the door latch and compress the weatherstrip.